The present invention is directed to a tool bit including a carrier member with a diamond-type or adamantine layer.
It is known in tools used for machining materials of various types, such as timber, rock, metal alloys and the like, to provide a carrier member with hard metal members. In machining operations using tool bit, the tool bits can be used for milling, boring, turning, or cutting with the carrier members having a correspondingly adapted shape. The hard metal or cutting metal members depending on the particular operation being performed, can be connected with the end faces of carrier member, such as by soldered connections.
It is known from patent publication EP-A 0 306 077 for increasing resistance to wear, to cover the hard metal member with one or several layers of metallic boron nitride with the boron concentration kept below a specific value. These layers act as a sort of diffusion block. In such members it is essential that the hardness of the applied layer is greater than that of the subjacent hard metal layer, whereby the cover layer has to be self-supporting. To afford this self-supporting property, the cover layer must have a relatively great thickness in the range of 1 to 10 micrometers. Such a great thickness involves internal or residual stress, whereby the layer is fracture and crackprone, especially to yielding of the softer subjacent layer or support base.
When machining or working on timber, aluminum alloys, rock and the like the use of tool bits with a diamond-type or adamantine layer have been used for affording a high resistance to wear. In such tools a carrier member is employed corresponding to the type of machining operation to be carried out.
The diamond-type or adamantine layer can be in different forms. The layer can be applied to the carrier member by known polyvinyldichloride or chemical vapor deposition methods. Further, there is the possibility of arranging individual diamond grains, for instance by soldering or a galvanic method, formed on the carrier member. Polycrystalline diamond platelets have a hard metal base member with the diamond grains bonded to it or as a diamond layer.
While diamond-type layers are especially advantageous in the above-mentioned applications involving resistance to wear, there is the disadvantage that they cannot machine iron compositions or ferroalloys. When ferroalloys are being machined, an interaction occurs between the diamond-type layers containing carbon and the iron in such a way that chemical wear of the layer occurs. Such an interaction can occur if concrete with steel reinforcing has to be cut or drilled and such a tool bit with a diamond-type layer encounters the steel reinforcing. Since it is common to encounter steel reinforcement in most concrete structures, tool bits with diamond-type layers cannot be used.